The instant invention relates to methods and apparatus for erecting a drilling rig mast and more particularly to such methods and apparatus wherein the foot of the mast is pinned to a substructure to permit pivoting of the mast into position for drilling or other operations.
The typical drilling rig, in assembled condition, includes a substructure having a substantially vertical mast mounted on the top thereof. The mast includes at its top a crown block from which a traveling block is suspended via a wire line. A drawworks is mounted on the top of the substructure and is used to reel line in and out thereby raising and lowering the traveling block. In accordance with past methods and apparatus for assembling such a drilling rig, the substructure is erected on a base which rests on the ground with the drawworks being mounted on the top of the substructure. The lower end or foot of the mast is then pinned to a pair of shoes on the top of the substructure. Thereafter, wire from the drawworks is strung between the crown block and traveling block. A cable is attached to the traveling block and is looped over a pulley which is supported by a gin pole at the top of the substructure. The other end of the cable is secured to the mast adjacent the foot thereof. When line is reeled in by the drawworks, the mast pivots upwardly about the shoes until it is in a vertical position at which point it is secured to the top of the substructure for drilling or other operations.
The foregoing-described operation for erecting a drilling rig mast works satisfactorily for substructures having a reasonably low height. As the search for oil and gas has led to the drilling of deeper and deeper wells, the height of substructures has increased in order to accomodate the large pressure-controlled equipment which must be secured to the well head beneath the substructure. Generally speaking, the deeper the well, the taller the substructure will be. Substructures can be as tall as thirty-seven feet and above.
If the foot of a mast is pinned to the top of a tall substructure, the top of the mast angles downwardly toward the ground and, when considering the weight of the mast, presents a load which cannot be pivoted into an upright position by the drawworks. The end of the mast can of course be elevated to the same height as the substructure by placing it on a support so that the mast will be substantially parallel to the ground; however, providing a support sufficiently sturdy to support the end of the mast at the height of the substructure and placing the mast on the top thereof creates an involved and expensive additional step in the erection of the mast.
The instant invention provides an advantage over the above-described prior art technique in that a drawworks may be used to mount a mast on a relatively tall substructure without the disadvantages attendant in the above-described prior art technique.
The instant invention includes means for pivotally attaching the foot of the mast to the base of a substructure. The end of the mast is then pivoted upwardly and the foot of the mast is detached from the substructure. The foot of the mast is then raised upwardly until it is at the point on the substructure at which it is to be secured for drilling or other operations. The foot of the mast is then pivotally attached to the substructure at that point and the end of the substructure is pivoted upwardly until the mast is in the position in which it is to be used for drilling or other operations.